Document changes to make for windows
diff --git a/README.rst b/README.rst
index 004f094..14f725d 100644
--- a/README.rst
+++ b/README.rst
@@ -35,6 +35,8 @@
make check
+In order to build for a Windows platform, you should use WINDOWS_BUILD=1 if the target is Windows but the build environment is Unix-like (eg when cross-compiling, or compiling from an MSYS shell), and WINDOWS=1 if the build environment is a Windows shell.
+
Depending on your platform, you might run into some issues. Please check the Makefiles in *library/*, *programs/* and *tests/* for options to manually add or remove for specific platforms. You can also check `the mbed TLS Knowledge Base <https://polarssl.org/kb>`_ for articles on your platform or issue.
In case you find that you need to do something else as well, please let us know what, so we can add it to the KB.
